This invention relates to systems for extinguishing fires, and in particular to a system for adding liquid foam concentrate into water lines in predetermined proportions.
Conventional foam additive systems for fighting fires employ numerous mechanisms for supplying foam liquid concentrate via supply conduits to one or more of the discharge outlets of a water pump. The goal of such a system is to achieve xe2x80x9cbalanced flowxe2x80x9d between the fluid line, typically a water line; and the additive line, typically a foam concentrate supply line. At balanced flow, the system responds to high fluid flow with a correlatively high additive flow, and corresponds to low fluid flow with a relatively low additive flow. Thus, at high water flow, foam is added at an equal flow calculated to maintain a predetermined ratio of water to foam. The same is true for low flow.
xe2x80x9cBalanced flowxe2x80x9d is particularly important in the fire-fighting field, because the water to foam ratio is critical to optimize fire fighting efficiency based on the type of fire fuel that that is present. Ranges between 0.2%-6% of foam have been reported as optimal, depending on the composition and fuel of the target fire. Further complicating the task of balancing flow is the extremely variable water flows and pressures. Thus, the volume and pressure of foam must meet the varying pressure and volume of water being used.
An exemplary embodiment of an additive pump system is a hydraulically powered demand system that varies additive pump output in response to different readings from a flow meter installed in the water pump discharge line that measures water flow rate. In a xe2x80x9cflow ratexe2x80x9d system, balanced pressure is achieved by control of water flow and additive flow rates.
One such flow rate system is disclosed in U.S. Pat. No. 5,174,383 (1992) to Haugen et al. The water flow meter signal is processed by a controller, e.g., microprocessor. The microprocessor sends a signal to the additive pump, e.g., a positive displacement piston pump, to regulate the flow rate of the additive line. Further, a measure of the additive pump output is fed back to the microprocessor, e.g., a speed signal is sent from a tachometer coupled to the drive shaft of the additive pump, to maintain the additive flow rate at the proper proportion to the water flow rate.
Another flow rate system is disclosed in U.S. Pat. No. 5,765,644 (1998) to Arvidson. To maintain the additive flow rate at the proper proportion to the water flow rate, the additive pump provides a feedback signal from a magnetic pickup associated with a notched wheel coupled to the drive shaft of the additive pump. Alternatively, a flow meter may be employed to measure the additive flow rate downstream of the additive pump.
While prior art systems are capable of accurately maintaining a pre-selected ratio of additive to water, these systems typically employ expensive pumps, e.g., gear pumps. Further, these are complicated systems, with the complex nature of the system negatively impacting the system reliability and cost.
The need remains for simple, accurate, and cost-effective control and monitoring of additive line flow. To overcome shortcomings of the prior art, an improved system to accurately maintain a pre-selected ratio of additive to water is disclosed. The system employs a novel pump and hydraulic cylinder arrangement, including a linear variable displacement transducer (LVDT) to measure the position, and thereby determine the speed, of the additive pump. The system provides an accurate, yet simple, cost-effective proportioning system for maintaining a desired foam to water ratio.
One aspect of the invention provides an additive proportioning system for a firefighting vehicle. The system comprises a source of pressurized water, a source of additive, and a hydraulic pump. A water flow sensor is provided that is responsive to the source of pressurized water and configured to measure a water flow rate.
An actuator is fluidly connected to and driven by the hydraulic pump. An additive pump is mechanically coupled to the actuator and fluidly connected to the source of additive. The system further provides a pump displacement sensor configured to sense the position of the additive pump. The pump displacement sensor is in communication with the water flow sensor to maintain a pre-determined ration of additive to water.
In a preferred embodiment, the pump displacement sensor is a linear variable displacement transducer, the additive pump is a double acting piston pump, and the actuator is a hydraulic cylinder.
According to another aspect of the invention, the system further comprises a programmable logic controller.
According to another aspect of the invention, the system further comprises a proportioning valve in communication with a programmable logic computer.
According to another aspect of the invention, the additive is a thixotropic substance.
According to yet another aspect of the invention, the system provides multiple sources of additive.
According to another aspect of the invention, the system further comprises a means for mixing the additive with the water.
Another aspect of the invention provides an apparatus for mixing water and an additive in a firefighting vehicle. The apparatus comprises a programmable logic computer, a water flow sensor, and a hydraulic pump. The water flow sensor is responsive to a source of pressurized water and is electronically coupled to the controller. An actuator is fluidly connected to and driven by the hydraulic pump. An additive pump is mechanically coupled to the actuator and fluidly connected to a source of additive. An additive pump displacement sensor is configured to sense the position of the additive pump and is in communication with the controller.
In a preferred embodiment, the actuator is a hydraulic cylinder, the pump displacement sensor is a linear variable displacement transducer, and the additive pump is a double acting piston pump.
In a preferred embodiment, the controller provides communication between the water flow sensor, the proportioning valve, and the additive pump to maintain a pre-determined ratio of additive to water.
According to another aspect of the invention, the apparatus further comprises a proportioning valve fluidly connected to the hydraulic pump and the actuator. In a preferred embodiment, the proportioning valve is in communication with the controller.
According to another aspect of the invention, the apparatus further comprises a means for mixing the additive with the water.
According to another aspect of the invention, the controller adjusts the additive pump speed in response to the sensed direction of the additive pump.
Another aspect of the invention provides an additive proportioning apparatus comprising an actuator and an additive pump coupled to and driven by the actuator. The actuator is coupled to a linear variable displacement transducer that senses the position of the additive pump.
Another aspect of the invention provides a method of maintaining a desired additive to water ratio in a fire-fighting system. The method comprises the steps of inputting a pre-determined additive to water ratio into the controller; sensing the water flow rate; computing the additive flow rate by determining the position of a positive displacement piston pump at at least two defined intervals; computing the actual additive to water ratio based on the sensed water flow and additive flow rates; comparing the computed ratio with the input ratio; and adjusting the output of the positive displacement pump to substantially match the input ratio.
According to another aspect of the invention, the method further comprises the steps of re-sensing the water flow rate; re-sensing the additive flow rate; re-computing the actual additive to water ratio; re-comparing the computed ratio with the input ratio; and re-adjusting the output of the positive displacement pump.